Directional drilling requires great skill and a suitable repertoire of tools. Among the techniques used by a directional driller is the selection of a proper drill bit. When a particular drill bit is combined with a specific near-bit assembly, a unique and usually predictable turning behavior is obtained. However, if the driller desires to change this behavior, he must remove the drill string and drill bit from the hole and establish a new down-hole assembly.
Removing the drill string and bit from the hole is an expensive operation and may delay the drilling operation by more than a day.